Channel Definitions

Speed

Speed is a Doppler derived channel coming directly from our GNSS engine, this is the 2D speed and has no direction. This data is calculated directly at the reference antenna.

If IMU integration is on, speed will be filtered using a Kalman filter producing a less noisy channel. This is also lever arm compensated to eliminate the effect of body movement on the roof mounted measurement location of the GNSS antenna.

Also in the case that GNSS signal is lost the IMU will continue to provide speed data however this will degrade in accuracy over time. It is recommended not to use data that has been without GNSS for more than 10 seconds.

Longitudinal Acceleration

Longitudinal acceleration value derived by differentiating the longitudinal component of the Doppler derived Speed calculated at the reference antenna.

This measurement is independent of body pitch angle.

If IMU integration is on, LongAcc will be filtered using a Kalman filter producing a more noise free channel, that is also lever arm compensated to remove body pitch induced overshoot during high dynamic braking or acceleration. In the case that GNSS signal is lost the IMU will continue to provide acceleration data however this will degrade in accuracy over time. It is recommended not to use data that has been without GNSS for more than 10 seconds.

Lateral Acceleration

Lateral acceleration value derived by differentiating the Doppler derived Speed and Heading channels calculated at the reference antenna.

This measurement is independent of body roll angle.

If IMU integration is on, LatAcc will be filtered using a Kalman filter producing a more noise free channel, that is also lever arm compensated to remove body pitch induced overshoot during high dynamic braking or acceleration. In the case that GNSS signal is lost the IMU will continue to provide acceleration data however this will degrade in accuracy over time. It is recommended not to use data that has been without GNSS for more than 10 seconds.

Heading

Heading is a Doppler derived channel coming directly from the GNSS engine. This heading will be the ‘course over ground’ bearing at the antenna location with respect to North, irrespective of vehicle direction.  

If IMU integration is on, the Heading value will be filtered using a Kalman filter producing a more noise free channel that is also lever arm compensated to remove body pitch and roll induced overshoot during high dynamic manoeuvres.  In the case that GNSS signal is lost the IMU will continue to provide heading data however this will degrade in accuracy over time. It is recommended not to use data that has been without GNSS for more than 10 seconds.

Height

Height is a positional calculated channel using trilateration from four or more observed satellites. As such it is prone to drift as satellite signal paths are bent through the Earth’s upper Ionosphere . This culminates in a typical accuracy in an open area with respect to absolute position of +/- 3 m.

Instantaneous jumps in this channel can occur when a satellite signal is lost or gained.

If IMU integration is on, the Height value will be filtered using a Kalman filter producing a less noisy channel. IMU integration will oppose the instantaneous jump in position caused by a satellite signal loss or gain.

Lever arm compensation is also applied to remove the overshoot of position caused by the effect body movement.

In the case that GNSS signal is lost the IMU will continue to provide height data however this will degrade in accuracy over time. It is recommended not to use data that has been without GNSS for more than 10 seconds.

Relative Height

This an integration of Vertical Velocity performed by the VBOX Tools/ VBOX Test Suite software when a logged file is loaded. It will be zero at the beginning of the file.

This channel has a very high height accuracy over short periods of time and is resilient to satellites appearing or disappearing .

Vertical Velocity

Vertical speed is a Doppler derived channel; it has a direction associated (+ve when climbing, -ve when descending).

If IMU integration is on, the Vertical speed value will be filtered using a Kalman filter producing a less noisy channel. In the case that GNSS signal is lost the IMU will continue to provide vertical speed data however this will degrade in accuracy over time. It is recommended not to use data that has been without GNSS for more than 10 seconds.

Satellites

Lists the total number of satellites the unit is currently tracking by adding the channels GPS satellites and GLONASS satellites. This excludes SBAS satellites and cannot exceed 31.

Glonass Satellites

Lists the total number of GLONASS satellites the unit is currently tracking in the solution. This Excludes SBAS satellites.

GPS Satellites

Lists the total number of GPS satellites the unit is currently tracking in the solution. This Excludes SBAS satellites.

Brake Trigger

The brake trigger is an oversampled digital input that is used for identifying exactly when the brake pedal is pressed for brake testing or event marking.

Position Latitude

Latitude is a geographic coordinate that specifies the north-south position of a point on the Earth's surface. Latitude is an angle produced in the GNSS engine using trilateration of satellite time signals from four or more observable satellites. Latitude ranges from 0° at the Equator to 90° (North or South) at the poles.

This will be augmented and ‘lever arm compensated’ using inertial data if an IMU is present and IMU integration switched on.

Position Longitude

Longitude is a geographic coordinate that specifies the east-west position of a point on the Earth's surface. It is an angle produced in the GNSS engine using trilateration of satellite time signals from four or more observable satellites. Longitude ranges from 0° at the prime meridian to 180° east and west.

This will be augmented and ‘lever arm compensated’ using inertial data if an IMU is present and IMU integration switched on.

DGPS

This channel indicates if the GPS is currently using a DGPS correction data to mitigate for GPS positional propagation errors. An improvement in the positional accuracy of the VBOX depends on what type of DGPS message is being used.

UTC Time

UTC is the universal coordinated time, which is accurate to about a nanosecond (billionth of a second) per day.

Distance

This channel is the accumulative total of distance in metres since the start of the file. This channel is calculated via integration of speed, so is a derivative of a Doppler derived channel.

Time

This channel is the accumulative total of time in seconds since the start of the file.

Radius of Turn

The Radius of Turn channel is derived from the speed and lateral acceleration channels. As IMU integration has an effect on both of these channels, the radius of turn data will also be smoother when IMU integration is enabled.

The Radius of Turn channel is calculated in the following way...

Abs((360 / RateOfChangeOfHeading) * speed / (2 * Math.PI))

Speed Quality

This is an RMS indication of the quality/accuracy of the current measured GNSS speed. It is expressed in km/h.

Centre Line Deviation

This is a measurement vehicle lateral movement (m). This parameter uses a previously sampled test lane heading as a reference and then from the start of each test creates a lateral deviation measurement. So if the vehicle pulls left during a brake stop then this parameter will display a +ve value in metres.

Position Quality

A numerical position confidence indicator used for RTK robot path following applications.

10 = Difference between GNSS and KF estimated position is better than 5 cm.
9 = Difference between GNSS and KF estimated position is between 5–10 cm.
8 = Difference between GNSS and KF estimated position is between 10 cm and 1 m.
7 = Path following position confidence is between 1–2 m.
2 = When the IMU filter has been enabled and IMU has sync'd but is not yet initialised. Once initialised it should report as per the above values.
1 = When the IMU has not sync'd or if the KF has not been enabled (note if KF has not been enabled, then the value will only be present on CAN).

Solution Type

A numerical representation of the mode of DGNSS correction currently being employed by the GNSS receiver:-

0 = None
1 = Stand alone
2 = GNSS DGNSS (inc RTCMv2 40 cm)
3 = RTK Float
4 = RTK Fixed
5 = Fixed position
6 = IMU Coast (Kalman Filter)

Lateral Velocity LatVel is the speed of the vehicle with respect to lateral direction of the vehicle body (90o to the direction of travel): It is derived from GNSS speed and Slip angle; GNSS speed is the speed of the vehicle in the direction of travel of the GNSS antenna.   The CAN channel is calculated in the following way... Lateral Velocity = Speed x Sin (Slip angle) Lat and Long Velocity relationship to slip angle: Slip angle = Arctan(Lateral velocity/Longitudinal velocity) When being used in single antenna mode, Slip angle is calculated as: Slip Angle = Robot Head – Heading

Longitudinal Velocity LngVel is the speed of the vehicle with respect to longitudinal direction of the vehicle body: It is derived from GNSS speed and Slip angle; GNSS speed is the speed of the vehicle in the direction of travel of the GNSS antenna.   The CAN channel is calculated in the following way... Longitudinal Velocity = Speed x Cos (Slip angle)   Lat and Long Velocity relationship to slip angle: Slip angle = Arctan(Lateral velocity/Longitudinal velocity)   When being used in single antenna mode, Slip angle is calculated as: Slip Angle = Robot Head – Heading

Yaw Rate

Degrees /second measurement from a gyro in the YAW plane of a vehicle. +ve clockwise.

X Accel

Accelerometer measurement in the vehicle longitudinal plane, +ve for forward acceleration. This measurement is not compensated for gravitational influence.

Y Accel

Accelerometer measurement in the vehicle lateral plane, +ve for acceleration to the left. This measurement is not compensated for gravitational influence.

Z Accel

Accelerometer measurement in the vehicle vertical plane, +ve for upward acceleration. This measurement is not compensated for gravitational influence.

Temp

Value of temperature from the IMU internal temperature sensor, NOT ambient temperature measurement.

Pitch Rate

Rotational rate measurement from a gyro in the longitudinal axis of a vehicle. -ve nose down.

Roll Rate

Rotational rate measurement from a gyro in the lateral axis of a vehicle. +ve for counter clockwise rotation.

True Heading

This is a measurement of heading from the reference antenna to the secondary antenna with respect to north. When mounted on a vehicle it becomes the measurement of heading that the vehicle is facing.

Slip Angle

The difference between Heading and Slip_Head channels. This is then a measurement of body slip angle at the reference antenna.

As IMU integration has an effect on the heading value, IMU integration will result in a less noisy Slip_Angle channel, it will also translate the measurement from the antenna location to the IMU location.

Note: If Dual Antenna lock is not valid and IMU integration is not active, no Slip Angle calculations will be made.

Pitch Angle

Pitch Angle is the angle between the two GNSS antennas when configured in “Pitch mode”. This channel gives an accurate measurement of absolute vehicle pitch relative to a zero line. As it is a direct angular measurement, it does not suffer drift over time.

Lateral Velocity The speed of the vehicle with respect to lateral direction of the vehicle body (90o to the direction of travel): It is derived from GNSS speed and Slip angle; GNSS speed is the speed of the vehicle in the direction of travel of the GNSS antenna.   The VB3iSL's Lat_Vel (Lateral velocity) CAN channel is calculated in the following way... Lateral Velocity = Speed x SIN (Slip angle)     Lat and Long Velocity relationship to slip angle: Slip angle = Arctan(Lateral velocity/Longitudinal velocity)

Longitudinal Velocity The speed of the vehicle with respect to longitudinal direction of the vehicle body: It is derived from GNSS speed and Slip angle; GNSS speed is the speed of the vehicle in the direction of travel of the GNSS antenna.   The VB3iSL's Long_Vel (Longitudinal velocity) CAN channel is calculated in the following way... Longitudinal Velocity = Speed x COS (Slip angle)     Lat and Long Velocity relationship to slip angle: Slip angle = Arctan(Lateral velocity/Longitudinal velocity)

Latitude_raw

This contains the raw GNSS Latitude value derived from positional data.

Longitude_raw

This contains the raw GNSS Longitude value derived from positional data.

Height_raw

This contains the raw GNSS height value derived from positional data.

Speed_raw

This contains the raw GNSS data from the Doppler derived GNSS Speed.

Vertical_Velocity_raw

This contains the raw GNSS data from the Doppler derived vertical Speed.

Heading_raw

This channel contains the raw GNSS data from the Doppler derived GNSS Heading.

IMU Kalman

This channel indicates the Kalman Filter status in numerical form.

RMS_HPOS

Accuracy of the current GNSS horizontal positional measurement.

RMS_VPOS

Accuracy of the current GNSS vertical positional measurement.

RMS_HVEL

Accuracy of the current GNSS horizontal velocity measurement

RMS_VVEL

Accuracy of the current GNSS vertical velocity measurement.

Head_imu

Head_imu is the heading of the body of the vehicle generated by the Kalman filter using GNSS and Inertial data. This is the IMU integration equivalent of twin antenna ‘True Heading’.

Pitch_imu

Pitch_imu is the pitch angle measured in degrees, generated from the Kalman filter using GNSS and inertial data.

Roll_imu

Roll_imu is the roll angle measured in degrees, generated from the Kalman filter using GNSS and inertial data.

Lng_Jerk

Longitudinal Jerk is the rate of change of GNSS longitudinal acceleration, generated from the Kalman filter, includes 0.5 s of smoothing.

Lat_Jerk

Lateral Jerk is the rate of change of GNSS lateral acceleration, generated from the Kalman filter, includes 0.5 s of smoothing.

Head_imu2

Head_imu2 is the heading of the body of the vehicle generated by the Kalman filter utilizing alignment algorithms and using GNSS and Inertial data.